This invitation to lecture to the Swindon Branch of the Society coincided with a period of crisis and change in the air transport industry where events stemming from growth, new technology, commercial challenge and political action were bringing about unprecedented ferment. Admittedly it could be said that the manufacturing industry has known this condition continuously for 20 years. But whereas the manufacturing industry has run into problems arising from retrenchment in military procurement, there is no sign that commercial air transport will do other in the long term than continue to expand. The main question is, what is the most beneficial nature of the expansion? A correct analysis of the present situation is important to the transport industry and also to the design and manufacturing organisations that are interested in building aircraft to meet the needs of the expansion ahead.

A favourite device of lecturers is to take a key word in the title of their speech and quote its definition from the pages of Webster's dictionary. Even though this may be mildly insulting to the audience—especially if the word being defined is something simple like “aviation”—it immediately gets the listeners onto the same track with the speaker. If nothing else, it proves the speaker at least knows how to spellthe key word in his speech and establishes his credentials as an expert in the field being discussed.

I would like to show you how informed I am by starting with a Webster's dictionary definition of “general aviation”, the key element in my speech title. Unfortunately, I cannot find it in my dictionary, and I doubt if you can find it in your Oxford dictionary. In the eyes of the lexicographers, “general aviation” simply does not exist. But you and I know it doesexist, and I would still like to start with a definition of it.

Much has been said and written about the last-minute preparation of the Royal Air Force for war after Munich, and of how disaster was so narrowly averted by inspired activity to produce fighters and train fighter pilots. Albeit there was more than a little luck on our side in the inability of the enemy to exploit a unique opportunity to attack this country immediately upon the outbreak of war in September 1939. We really were too weak to have stopped them at that time.

We were not only unprepared in numbers, but also to some extent in terms of tactical thinking and training. One of my earliest recollections of the Service was finding with something of a shock that as a newcomer, and at 18 scarcely more than a schoolboy, I had different ideas about the tactical use of fighters to those being taught at the time.

The principle of wall similarity expressed by a universal logarithmic inner law relationship is well established for turbulent flow in circular pipes. The validity of Preston's original hypothesis for the measurement of turbulent skin friction depends upon the existence of wall similarity. Although Preston's hypothesis appears to be correct in general it has been found that his calibration for the wall pitot tube was incorrect. Extensive observations by Head and Rechenberg showed some discrepancy. Later work by Patel on the measurement of skin friction in three circular pipes covering a much larger experimental range has led to a modified calibration.

Wind tunnels are far older than powered flight. Including the aeroplane of the Wright Brothers, the introduction of new types of aircraft has almost invariably been preceded by extensive model investigation in wind tunnels. These investigations can be classified into two broad areas. One is development testing, in which models are tested and modified with the purpose of producing a specific aircraft configuration. The other covers the research and general experimentation which is necessary for the determination of the new rules governing entry into a new régime of flight. Thus, wind tunnels may conveniently be referred to either as “development” or as “research” wind tunnels, according to the type of work which is done in them.

At the beginning of manned flight, aircraft needed some length of ground run in order to take off and fly. The Wrights took under 60 ft, and with a wing loading of 1.47 lb/sq ft and a CL max of approximately 0.9 they achieved first manned flight.

Time went on, and man grew more familiar with the hazards of increased take-off length and take-off speed. His growing knowledge of aerodynamics allowed him to increase the CL max values on wings. These facts combined to allow him to use increased wing loadings to improve his flight efficiency in terms of payload, cruise speed and range. The following graphs show the growth of these characteristics.